cAMP-dependent protein kinase in chondrocyte cultures: holoenzyme activation, phosphorylation of cellular proteins, effects of NSAIDs and possible role in proteoglycan synthesis

Induction of apoptosis in bovine articular chondrocyte by prostaglandin E(2) through cAMP-dependent pathway

OBJECTIVE

Regulation of important biological processes such as proliferation and differentiation of articular chondrocytes is known to be mediated by prostaglandin E(2) (PGE(2)) in both normal and pathological states. Articular chondrocytes also undergo apoptosis, a biological phenomenon implicated in many physiological processes. Whether or not PGE(2) induces apoptosis in articular chondrocytes, however, is not known.

DESIGN

Bovine articular chondrocytes were cultured with or without PGE(2) for 24 h and amounts of fragmented DNA, which is a distinct characteristic of apoptosis, were measured by enzyme-linked immunosorbent assay. Also effect of cyclic AMP (cAMP), which is one of the intracellular downstream mediator of PGE(2), on chondrocyte apoptosis was investigated.

RESULTS

Administration of exogenous PGE(2) on bovine articular cartilage grown as a monolayer culture resulted in the induction of DNA fragmentation. This DNA fragmentation was accompanied with a marked dose-dependent increase in intracellular cAMP. Also cultured cells were treated with cAMP analogue, dibutyryl-cAMP or forskolin, a direct activator of adenylate cyclase, and the incidence of apoptosis in the chondrocytes was determined. As well as PGE(2), dibutyryl-cAMP and forskolin stimulated chondrocyte DNA fragmentation.

CONCLUSIONS

It is the first report that PGE(2) can induce articular chondrocyte apoptosis in vitro. It is also suggest that apoptosis of chondrocytes by PGE(2) is linked with cAMP-dependent pathway.